Guest user only boot up

When at the login screen showing just the Guest user hold down Option or alt and the right arrow key. It will populate more users if they exist.

If that doesn't work you can boot into either single user mode (guide to boot to single user) or Restore partition and open terminal.app and run this command:

defaults write /Library/Preferences/com.apple.loginwindow SHOWFULLNAME -bool yes

This will change the login window to be the name and password field. Then you can enter your username.

Restart in recovery mode, open terminal and type "resetpassword" - follow instructions and this will allow you to reset your user pw.

Try safe mode. Here are the instructions, from the Apple Support website:

Be sure your Mac is shut down.

1. Press the power button.
2. Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone, but not before the tone.
3. Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).

Once you are in, go to System Preferences and disable Find My Mac (iCloud settings) and Guest User (Users and Groups). Reboot. You should be able to login normally.